The field of the invention is the preparation of unsaturated alcohols and the present invention is particularly concerned with the preparation of cyclooctene-4-ol-1.
A. C. Cope et al disclose the state of the art production of cyclooctene-4-ol-1 in the Journal of the American Chemical Society, Volume 81 (1959), pages 1643-1650, the disclosure of which is incorporated herein.
According to this state of the art, cyclooctene-4-ol-1 is prepared by adding 1 mole of formic acid in the presence of perchloric acid to 1 mole of cis-cis-1,5-cyclooctadiene in a first stage. Thereupon the reaction products are saponified and reprocessed by a careful fractional distillation. To separate the saturated alcohols, which are formed in large amounts, from the desired cyclooctene-4-ol-1, an expensive extraction with a 20% aqueous silver nitrate solution must be resorted to. The yield in cyclooctene-4-ol-1 in this costly process amounts to only 20%.
The uncatalyzed addition of formic acid to other olefins is known, though not to cyclooctadiene-1,5 as reported by H. B. Knight, R. E. Koos and D. Swern in the Journal of the American Chemical Society, Volume 75 (1953) at page 6212. As regards the uncatalyzed reaction, a conversion of only 80% is obtained after 24 hours at the boiling point of the formic acid. By adding slight amounts of perchloric acid (0.5 to 2% by weight referred to olefin), the reaction time can be reduced to 5 to 15 minutes.
1 Mol of vinylcyclohexene, which is an isomer of cyclooctadiene-1,5, reacts with 3 moles of formic acid according to the procedure disclosed in U.S. Pat. No. 2,764,610 (8 hours at 94.degree. to 97.degree. C. with reflux) with a conversion of 44%.
The yield in monoformic acid esters referred to the converted vinylcyclohexene amounts to only 61%.
Accordingly, all the prior art processes provide only slight yields, require long reaction times or make use of catalysts which require reprocessing and ecological problems.